1. (Field of the Invention)
The present invention relates to a sensor-incorporated wheel support bearing assembly equipped with a load sensor for detecting a load acting on a bearing portion of a wheel.
2. (Description of the Prior Art)
For safety travel of an automotive vehicle, the wheel support bearing assembly equipped with a sensor for detecting the rotational speed of one of automotive wheels has hitherto been well known in the art. While the automobile traveling safety precaution is hitherto generally taken by detecting the rotational speed of a wheel of various parts, but it is not sufficient with the detection of only the rotational speed of the wheel and, therefore, it is required to achieve a safety control of the automotive vehicle with the use of other sensor signals.
In view of this, it may be contemplated to achieve an posture control based on a load acting on each of wheels during travel of an automotive vehicle. By way of example, a large load acts on the outside wheels during the cornering, on the wheels on one side during the run along left and right inclined road surfaces or on the front wheels during the braking and, thus, a varying load acts on the vehicle wheels. Also, in the case of the uneven live load, the loads acting on those wheels tend to become uneven. For this reason, if the loads acting on the wheels can be detected as needed, suspension systems for the vehicle wheels can be controlled beforehand based on results of detection of the loads so that the posture control of the automotive vehicle during the traveling thereof (for example, prevention of a rolling motion during the cornering, prevention of downward settling of the front wheels during the braking, and prevention of downward settling of the vehicle wheels brought about by the uneven distribution of live loads) can be accomplished. However, no space for installation of the load sensor for detecting the load acting on the respective vehicle wheel is available and, therefore, the posture control through the detection of the load can hardly be realized.
Also, in the event that in the near future the steer-by-wire is introduced to provide the system, in which the wheel axle and the steering come not to be coupled mechanically with each other, and such system is increasingly used, information on the road surface comes to be required to transmit to the steering wheel held by a driver by detecting a load acting in a wheel axis direction.
In order to meet those needs, the wheel support bearing assembly has been suggested, in which a strain gauge is affixed to an outer race of the wheel support bearing assembly so that the strain gauge can detect a strain acting on the outer race. (See, for example, the Japanese Laid-open Patent Publication No. 2003-530565, published Oct. 14, 2003).
The outer race of the wheel support bearing assembly has at least one raceway surface defined therein and therefore must have a sufficient strength. And also the outer race of the wheel is manufactured through complicated process steps including metal forming, turning, heat treatment, and grinding. Thus, affixation of the strain gauge to the outer race as described in the patent document No. 2003-530565 is not efficient in productivity and is costly when it comes to mass production thereof. Furthermore, it is difficult to detect a strain on the outer race with good sensitivity.
A strain sensor such as the strain gauge is thus affixed to a sensor mounting member to form a sensor unit, which is fitted to the peripheral surface of the outer race to enhance productivity and to improve detection sensitivity. According to such configuration, fitting the strain sensor to the outer race is facilitated, and a strain larger than that on the outer strain appears at the sensor mounting member, whereby the strain on the outer race can be detected with good sensitivity.
However, when the strain sensor unit is fitted in this manner, the temperature of the sensor mounting member varies with the temperature of the wheel support bearing assembly, which changes during the traveling thereof, thus affecting the strain of the sensor mounting member and the operation of the sensor. It is important in carrying out an appropriate posture control to remove such affect of the temperature and to assuredly detect a load acting on each wheel with sufficient accuracy. It is also preferred to detect the abnormal change in temperature of the wheel support bearing assembly so that when faults occur at the wheel support bearing assembly, such faults can be found.
In addition to the sensor for detecting a load, such as the strain gauge, a sensor for detecting an angle of rotation or a direction of rotation of the wheel support bearing assembly can be provided on the wheel support bearing assembly. In this case, the sensor for detecting an angle of rotation is also required to be affixed with low cost, similar to the sensor for detecting a load. It is desirable that both sensors for detecting a load and for detecting an angle of rotation are easily affixed, and wiring for connecting the sensors and a circuit for processing the detected signals by the sensors is not complicated.
In the meanwhile, the wheel support bearing assembly is a component of an automotive vehicle used under various severe conditions. Thus, in order to appropriately carry out various controls and determination of wheel lifespan and maintenance necessity of the automotive vehicle, some statuses of the wheel support bearing assembly must be accurately detected. The status of the wheel support bearing assembly to be detected may include an acceleration of rotation, a vibration, and whether or not water ingress into the bearing assembly space has occurred. By detecting the acceleration, the automotive vehicle can be more appropriately controlled. The vibration is one of the most important factors in determining the bearing lifespan. Water ingress greatly influences degradation of grease. It is desirable for the wheel support bearing assembly to employ a unit for detecting such status at low cost without complicating the detection system.